FIG. 1 diagrammatically illustrates the overall configuration of a conventional multi T1 radio at a transmit site 1, and comprising a multiplexer 10 to which a plurality of T1 channels (e.g., 4 in the illustrated example) are applied. For the sake of simplicity, let it be assumed that each channel is a 1.544 Mbps channel. The output of multiplexer 10 is coupled to a rate ½ convolutional encoder 12, the output of which is encoded into IQ space (QPSK) and coupled through a convolutional interleaver 14 for application to an RF unit 16, from which the encoded data stream is wirelessly transmitted to a receiver site 2. At the receiver site 2, the wirelessly transmitted modulation is downconverter to baseband by an RF front end 21 and then supplied to a deinterleaver 23 for application to a rate ½ Viterbi decoder 25. The output of the Viterbi decoder is coupled to a demultiplexer 27 from which the T1 data is demultiplexed.
In the example, convolutional encoder 12 being a rate ½ encoder implies that two bits are transmitted for each input bit, so that in the QPSK constellation space, there is an effective symbol rate of 6.44 M symbols/sec. At the receive end of the link, the output of the rate ½ Viterbi decoder 25 is a 6.44 Mbps data stream that is coupled to demultiplexer 27, from which the four original T1 channels are recovered. Where it is desired to transmit a different number of T1 channels, it has been traditional practice to employ a different radio whose parameters are defined for the purpose, and which contains the appropriate replacement filter set.